The present invention relates to the general field of fluid transport pipes, and in particular to undersea pipes, resting on the sea bottom or providing a bottom-to-surface connection for transferring hydrocarbons, e.g. oil and gas, coming from undersea production wells.
The invention relates to pipes of all types, and in particular to coaxial pipes of the pipe in pipe (PIP) type, where an inner tube transports the fluid and an outer tube coaxial around the inner tube, and also referred to as the “outer envelope”, is in contact with the surrounding medium, i.e. water.
In general, these coaxial pipes are assembled on land to constitute elements of unit length (known as double, triple, or quadruple joints, and referred to below as “quad-joints” for quadruple sections of tube), having length of the order of 10 meters (m) to 100 m, depending on the loading capacity of the laying system. Such quad-joints are then transported to sea on a laying vessel.
During laying, the quad-joints are connected to one another on board the vessel while they are being laid at sea. Laying may be performed via a J-lay tower positioned on the laying vessel. With J-laying, the undersea pipe is typically lowered from the laying vessel practically vertically (at an angle in the range +30° to −10° relative to the vertical). J-laying comprises simple catenary laying in which the quasi-vertical angle of inclination of the pipe diminishes progressively on going down towards the bottom where it matches the slope of the sea bottom.
The J-laying method makes it necessary to move each quad-joint from a horizontal position (along the deck of the laying vessel) to a vertical position in order to align it with the J-lay tower. The quad-joint is held vertically by the laying tower in order to enable its bottom end to be welded to the top end of the pipe. Once the quad-joint has been welded to the pipe, the quad-joint is lowered into the sea while moving the laying vessel forwards by an amount corresponding to the length of the quad-joint.
Furthermore, it is known to place cables in the annular space between the two tubes of such undersea coaxial pipes so that the cables run along the inner tube over their entire length.
These cables are constituted in particular by electric cables that are wound around the inner tubes of pipes in order to heat them by the Joule effect. This technique is known as heat tracing and serves to ensure that the fluids transported in undersea pipes are maintained at a temperature above a critical threshold all along their paths from the production well to a surface installation (so as to avoid the appearance of troublesome phenomena in the pipes and so as to maintain good flow conditions).
Unfortunately, when J-laying a new quad-joint on the undersea pipe, the problem arises of making connections between the cables of the pipe and the cables of the new quad-joint. Given the vertical position of the tubes during such laying, it is necessary in particular to ensure that connecting the cables is simple, fast, and effective.